White light emitting LEDs (“white LEDs”) are known and are a relatively recent innovation. It was not until LEDs emitting in the blue/ultraviolet part of the electromagnetic spectrum were developed that it became practical to develop white light sources based on LEDs. As taught, for example in U.S. Pat. No. 5,998,925, white LEDs include one or more one or more photoluminescent materials (e.g., phosphor materials), which absorb a portion of the radiation emitted by the LED and re-emit light of a different color (wavelength). Typically, the LED chip or die generates blue light and the phosphor(s) absorbs a percentage of the blue light and re-emits yellow light or a combination of green and red light, green and yellow light, green and orange or yellow and red light. The portion of the blue light generated by the LED that is not absorbed by the phosphor material combined with the light emitted by the phosphor provides light which appears to the eye as being nearly white in color. Alternatively, the LED chip or die may generate ultraviolet (UV) light, in which phosphor(s) to absorb the UV light to re-emit a combination of different colors of photoluminescent light that appear white to the human eye.
Due to their long operating life expectancy (>50,000 hours) and high luminous efficacy (70 lumens per watt and higher) high brightness white LEDs are increasingly being used to replace conventional fluorescent, compact fluorescent and incandescent light sources.
Typically the phosphor material is mixed with light transmissive materials, such as silicone or epoxy material, and the mixture applied to the light emitting surface of the LED die. It is also known to provide the phosphor material as a layer on, or incorporate the phosphor material within, an optical component, a phosphor wavelength conversion component, that is located remotely to the LED die (“remote phosphor” LED devices).
FIG. 1 shows one possible approach that can be taken to implement a lighting device 100 when using a wavelength conversion component 102. The wavelength conversion component 102 includes a photoluminescence layer 106 having phosphor materials that are deposited onto an optically transparent substrate layer 104. The phosphor materials within the photoluminescence layer 106 generate photoluminescence light in response to excitation light emitted by an LED die 110. The LED die 110 is attached to a MCPCB 160. The wavelength conversion component 102 and the MCPCB 160 are both mounted onto a thermally conductive base 112.
The wavelength conversion component 102 is manufactured to include a protruding portion 108 along the bottom. During assembly of the lighting device 100, the protruding portion 108 acts as an attachment point that fits within a recess formed by mounting portion 116 of the thermally conductive base 112.
To increase the light emission efficiency of the lighting device 100, a reflective material 114 is placed onto the thermally conductive base 112. Since the light emitted by the phosphor materials in the photoluminescence layer 106 is isotropic, this means that much of the emitted light from this component is projected in a downwards direction. As a result, the reflective material 114 is necessary to make sure that the light emitted in the downwards direction is not wasted, but is instead reflected to be emitted outwardly to contribute the overall light output of the lighting device 100.
One problem with this approach is that adding the reflective material 114 to the base 112 requires an additional assembly step during manufacture of the lighting device. Moreover, significant material costs are required to purchase the reflective material 114 for the light assembly. In addition, it is possible that the reflective surface of the reflective material 114 may end up damaged during shipping or assembly, thereby reducing the reflective efficiencies of the material. An organization may also incur additional administrative costs to identify and source the reflective materials.
Another problem with this type of configuration is that light emitted from the lower levels of the photoluminescence layer 106 can be blocked by the mounting portion 116 on the base 112. This effectively reduces the lighting efficiency of the lighting device 100. Since phosphor materials are a relatively expensive proportion of the cost of the lighting device, this wastage of the light from the lower portions of the wavelength conversion component 102 means that an excessive amount of costs was required to manufacture the phosphor portion of the product without receiving corresponding amounts of lighting benefits.